Fluid flow sensor and method of fabricating the same

ABSTRACT

In a sensor chip for a fluid flow sensor, a thin film portion is formed above a hollow cavity portion while leaving thin film layers formed on the surface of a substrate. A conductor is provided on the inner wall face of a through hole formed to penetrate the substrate to thereby electrically connect a detecting portion constituted by a conductor film in the thin film layers and a substrate conductor portion formed on the rear face side of the through hole. The surface of a circuit board is formed with a control circuit and a base conductor portion electrically connected to the control circuit. The sensor chip and the circuit board are layered and the substrate conductor portion and the base conductor portion are electrically connected.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is based on and incorporates herein by referenceJapanese Patent Applications No.2001-101593 filed Mar. 30, 2001 and No.2001-376176 filed Dec. 10, 2001.

FIELD OF THE INVENTION

[0002] The present invention relates to a fluid flow sensor and a methodof fabricating the same fabricated by a semiconductor process.

BACKGROUND OF THE INVENTION

[0003] One type of a conventional thermal fluid flow sensor for use indetecting flow amount of air is disclosed in U.S. Pat. No. 5,404,753(JP-A-6-50783). In this thermal fluid flow sensor, a thin filmsemiconductor flow detecting part and a bonding pad (conductor part) areprovided on the same plane and separated from each other by a separationwall. As a result, it is not possible to reduce the planar size of thefluid flow sensor.

SUMMARY OF THE INVENTION

[0004] It is an object of the invention to provide a fluid flow sensorcapable of reducing its planar size and a method of fabricating thesame.

[0005] In one of preferred embodiments, a fluid flow sensor comprises afluid flow sensor chip that includes a board and detecting portionsformed on a first surface of the board for detecting a flow rate offluid flowing above the first surface of the board. The fluid flowsensor chip further includes a substrate conductor portion electricallyconnected to the detecting portions and formed on a surface other thanthe first surface.

[0006] In fabricating the fluid flow sensor, thin film layers are formedabove the first surface of the board, and a hollow cavity portion isformed by etching the board from the side of a second surface of theboard opposite the first surface. A through hole is formed in the boardwhere the hollow cavity portion is not formed. A conductor is formed onan inner wall face of the through hole to form a substrate conductorportion on the side of the second surface of the board.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The above and other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

[0008]FIG. 1 is a sectional view showing a fluid flow sensor accordingto a first embodiment of the present invention;

[0009]FIG. 2 is a top view showing the fluid flow sensor according tothe first embodiment;

[0010]FIG. 3A through FIG. 3E are sectional views showing a part of amethod of fabricating the fluid flow sensor according to the firstembodiment;

[0011]FIG. 4 is a sectional view showing a fluid flow sensor accordingto a second embodiment of the present invention;

[0012]FIG. 5 is a sectional view showing a fluid flow sensor accordingto a third embodiment of the present invention;

[0013]FIG. 6 is a perspective view schematically showing the fluid flowsensor according to the third embodiment;

[0014]FIG. 7 is a sectional view showing a fluid flow sensor accordingto a fourth embodiment of the present invention;

[0015]FIG. 8 is a sectional view showing a fluid flow sensor accordingto a fifth embodiment of the present invention;

[0016]FIG. 9A through FIG. 9D are sectional views showing a part of amethod of fabricating a fluid flow sensor according to a sixthembodiment of the present invention;

[0017]FIG. 10A through FIG. 10C are sectional views showing another partof the method of fabricating the fluid flow sensor according to thesixth embodiment;

[0018]FIG. 11 is a sectional view showing a fluid flow sensor accordingto a seventh embodiment of the present invention;

[0019]FIG. 12 is a sectional view showing a fluid flow sensor accordingto a modification of the seventh embodiment;

[0020]FIG. 13 is a sectional view showing a fluid flow sensor accordingto an eighth embodiment of the present invention;

[0021]FIG. 14A through FIG. 14C are sectional views showing a part of amethod of fabricating a fluid flow sensor according to a ninthembodiment of the present invention;

[0022]FIG. 15A and FIG. 15B are sectional views showing a part of amethod of fabricating a fluid flow sensor according to a tenthembodiment of the present invention;

[0023]FIG. 16 is a sectional view showing a fluid flow sensor chipaccording to an eleventh embodiment of the present invention; and

[0024]FIG. 17 is a sectional view showing a fluid flow sensor accordingto a twelfth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The present invention will be described in detail with referenceto various embodiments, in which the same or similar reference numeralsare used to designate the same or similar parts.

[0026] (First Embodiment)

[0027] Referring to FIG. 1, a fluid flow sensor 100 according to thefirst embodiment is constructed with a fluid flow sensor chip 10, whichis electrically connected to a circuit board 20 constituting a basehaving a control circuit. The circuit board 20 is fixed to a base board30. This fluid flow sensor 100 may be provided in an intake air passageof an internal combustion engine for measuring intake air flow to theengine.

[0028] In the sensor chip 10, a lower film 2 comprising an insulatingfilm is formed on a surface 1 a of a substrate 1. A conductor film 3 isformed on the lower film 2, and an upper film 4 comprising an insulatingfilm is formed on the lower film 2 and the conductor film 3. Thus, athin film layer is constituted by combining the lower film 2, theconductor film 3 and the upper film 4. Specifically, the lower film 2 islayered with a nitride film and an oxide film in this order from theside of the substrate 1. A platinum (Pt) film is used for the conductorfilm 3. The upper film 4 is layered with an oxide film and a nitridefilm.

[0029] An insulating film 5, which is an oxide film or the like, isformed on the side of a rear face 1 b of the substrate 1 opposed to thesurface 1 a. A hollow cavity portion 6 is formed from an opening portionof the insulating film 5, while leaving the thin film layers 2 through4. Further, the thin film layers 2 through 4 above the hollow cavityportion 6 constitute a thin film portion 7.

[0030] As shown in FIG. 2, there are constituted a heater 3 a, atemperature measuring body 3 b, a fluid thermometer 3 c and an electrodelead-out portion 3 d. In this figure, a normal fluid flow direction isindicated by an arrow. Each of these is formed respectively in themeandering shape by the conductor film 3 in the thin film layers 2through 4. Among them, the heater 3 a, the temperature measuring body 3b and the fluid thermometer 3 c correspond to a detecting portion fordetecting a flow rate of a fluid. The heater 3 a and the temperaturemeasuring body 3 b are arranged at the thin film portion 7. The heater 3a, the temperature measuring body 3 b and the fluid thermometer 3 c arealigned in this order. The electrode lead-out portion 3 d iselectrically connected to the heater 3 a, the temperature measuring body3 b and the fluid thermometer 3 c, respectively, and is extended to anend portion of the surface 1 a of the substrate 1.

[0031] There are formed through holes 8 penetrating the surface and therear face 1 a and 1 b of the substrate 1 at portions of the substrate 1corresponding to end portions of the electrode lead-out portions 3 d.Specifically, the through hole 8 constitutes a hole opened at a side ofthe rear face 1 b of the substrate 1 and reaching the conductor film(electrode lead-out portion 3 d) 3 on a side of the surface 1 a of thesubstrate 1. A conductor 9 is provided on the inner wall face of thethrough hole 8 and is electrically connected to the conductor film 3 atthe surface 1 a of the substrate 1.

[0032] In the vicinity of the opening portion of the through hole 8 inthe rear face 1 b of the substrate 1, a substrate conductor portion 11is formed to be exposed from the side of the rear face 1 b of thesubstrate 1. The substrate conductor portions 11 are connected to theconductors 9 at insides of the through holes 8. As a result, thesubstrate conductor portions 11 are electrically connected to detectingportions 3 a through 3 c via the conductors 9. That is, at a face of anouter surface of the substrate 1 other than the surface 1 a (rear face 1b), there are formed the substrate conductor portions 11 electricallyconnected to the detecting portions 3 a through 3 c.

[0033] In the fluid flow sensor 100, a control circuit 21 forcontrolling the detecting portions 3 a through 3 c is formed at asurface 20 a of the circuit board 20. Further, a base conductor portion22 electrically connected to the control circuit 21 is formed at thesurface 20 a of the circuit board 20.

[0034] The sensor chip 10 is layered on the circuit board 20 byarranging the side of the surface 20 a of the circuit board 20 inopposition to the side of the rear face 1 b of the substrate 1 of thesensor chip 10 such that the surface 1 a of the substrate 1 of thesensor chip 10 and the control circuit 21 are prevented from beingarranged on the same plane. The base conductor portion 22 and thesubstrate conductor portion 11 are electrically connected by a bump 23.The bump 23 is a member having conductivity, having adhesive force andhaving strength as a structure. Specifically, the bump 23 comprisinggold or the like can be used.

[0035] As a result, the control circuit 21 and the detecting portions 3a through 3 c of the substrate 1 are electrically connected via theconductor 9 of the through hole 8, the substrate conductor portion 11and the base conductor portion 22. Further, a gap is formed between thesensor chip 10 and the circuit board 20 by the bump 23.

[0036] The rear face 20 b of the circuit board 20 is fixed to the baseboard 30. Specifically, the rear face 20 b of the circuit board 20 isattached to the base board 30 by an adhesive member 31 of epoxy resin orthe like. A casing or the like for containing the fluid flow sensor 100can be used as the base board 30.

[0037] Next, the method of fabricating the fluid flow sensor 100 will bedescribed in reference to FIGS. 3A through 3E, which are sectional viewsshowing a method of forming the through hole 8. The substrate 1 isprepared. After forming the lower film 2 on the surface 1 a of thesubstrate 1, the conductor film 3 is formed and the conductor film 3 ispatterned to thereby form the heater 3 a, the temperature measuring body3 b, the fluid thermometer 3 c and the electrode lead-out portion 3 d.Thereafter, the upper film 4 is formed on the conductor film 3 (step offorming thin film layers).

[0038] Successively, the hollow cavity portion 6 is formed by etchingthe substrate 1 until the thin film layers 2 through 4 are exposed, fromthe side of the rear face 1 b of the substrate 1 with the insulatingfilm 5 formed on the side of the rear face 1 b of the substrate 1 as amask. As a result, the thin film portion 7 is formed on the hollowcavity portion 6 (step of forming thin film portions).

[0039] Thereafter, as shown in FIG. 3A, a resist 41 is formed to openonly at a portion to be formed with the through hole 8 on the side ofthe rear face 1 b of the substrate 1. As shown in FIG. 3B, the throughhole 8 is formed by carrying out etching operation until the conductorfilm 3 in the thin film layers 2 through 4 is exposed with the resist 41as a mask (step of forming through hole). After successively removingthe resist 41, as shown in FIG. 3C, a conductor 42 is coated on theinner wall face of the through hole 8 and the rear face of the substrate1.

[0040] As shown in FIG. 3D, a resist 43 is formed at an inner portion ofthe through hole 8 and a surface of the portion for constituting thesubstrate conductor portion 11. By carrying out etching operation, theconductor 42 at a portion which is not covered by the resist 43 isremoved. Thereafter, the resist 43 is removed. As described above, stepsexplained in reference to FIG. 3C and FIG. 3D are steps of forming thesubstrate conductor portion.

[0041] The circuit board 20 formed with the control circuit 21 and thebase conductor portion 22 at the surface 20 a is prepared and as shownin FIG. 3E. The substrate conductor portion 11 and the base conductorportion 22 are electrically connected via the bump 23. Thereafter, thebase board 30 is prepared and the side of the rear face 20 b of thecircuit board 20 is fixed to the base board 30 by the adhesive member31.

[0042] According to the fluid flow sensor 100, the heater 3 a is drivento provide temperature higher than fluid temperature detected by thefluid thermometer 3 c. When the fluid is made to flow from the fluidthermometer 3 c toward the heater 3 a by flowing above the detectingportions 3 a through 3 c, the temperature measuring body 3 b is deprivedof heat and its temperature is lowered. When the fluid is made to flowfrom the heater 3 a toward the fluid thermometer 3 c, heat is conveyedto the temperature measuring body 3 b and its temperature is elevated.Therefore, a flow rate and a flow direction of the fluid can be detectedby outputting a temperature difference between the temperature measuringbody 3 b and the fluid thermometer 3 c from the electrode lead-outportion 3 d as a change in voltage or the like. The detecting portions 3a through 3 c are controlled mainly by the control circuit 21 in theknown manner.

[0043] According to this embodiment, the though hole 8 is formed at thesensor chip 10 and the conductor 9 is provided on the inner wall face ofthe through hole 8. Therefore, transmission and reception of electricsignals between the detecting portions 3 a through 3 c and the controlcircuit 21 can be carried out on the side of the rear face 1 b of thesubstrate 1. Therefore, it is not necessary to provide an electricconnecting portion between the detecting portions 3 a through 3 c andthe control circuit 21 on the surface 1 a of the substrate 1 in thesensor chip 10. Therefore, it is not necessary to protect the connectingportion against the fluid. The control circuit 21 is not arranged on thesame plane as that of the surface of the sensor chip 10. Therefore, thecontrol circuit 21 is not exposed to the fluid flowing above thedetecting portions 3 a through 3 c, and it is not likely that thecontrol circuit 21 is damaged by the fluid.

[0044] As a result, it is not necessary to arrange a partition wall forprotecting the connecting portion and the control circuit 21 above thesurface 1 a of the substrate 1. Therefore, there need not be provided anarea of arranging the partition wall nor an area between the detectingportions 3 a through 3 c and the partition wall which is needed in orderto restrain disturbance of flow of the fluid when the partition wall isarranged. Therefore, the planar size of the sensor chip 10 can bereduced.

[0045] A gap is provided between the sensor chip 10 and the circuitboard 20, outside of the fluid flow sensor 100 and the hollow cavityportion 6 are communicated with each other. Therefore, the thin filmportion 7 can be restrained from being destructed by reducing pressuredifference between the surface and the rear face of the thin filmportion 7 when the fluid flows above the thin film portion 7.

[0046] The substrate conductor portion 11 and the base conductor portion22 may electrically be connected by silver paste.

[0047] (Second Embodiment)

[0048] In the second embodiment shown in FIG. 4, the control circuit 21is formed on the side of the rear face 20 b of the circuit board 20.

[0049] As shown in FIG. 4, the control circuit 21 is formed on the sideof the rear face 20 b of the circuit board 20. A through hole 24 isformed to penetrate from the side of the surface 20 a to the side of therear face 20 b at the circuit board 20. The through hole 24 is providedat a position corresponding to the through hole 8 of the sensor chip 10.A conductor 25 is provided on an inner wall face of the through hole 24,and is electrically connected to a base conductor portion 22 provided onthe side of the rear face 20 b of the circuit board 20. A surfaceconductor portion 26 is exposed from the circuit board 20 at an openingportion of the through hole 24 also on the side of the surface 20 a ofthe circuit board 20. The surface conductor portion 26 is electricallyconnected to the conductor 25 at the inside of the through hole 24.

[0050] The side of the surface 20 a of the circuit board 20 is layeredto be arranged in opposition to the side of the rear face of the sensorchip 10. The substrate conductor portion 11 and the surface conductorportion 26 of the circuit board 20 are electrically connected by a goldbump 27 or the like. The side of the rear face 20 b of the circuit board20 is attached to the base board 30 of a casing or the like of the fluidflow sensor via the adhesive member 31 of the epoxy resin or the like.

[0051] According to this second embodiment, not only the circuit board20 can be fixed to the base board 30 but also the control circuit 21 canbe protected against a surrounding environment by molding the controlcircuit 21 by the adhesive member 31. Since the control circuit 21 canbe protected without particularly adding a step of protecting thecontrol circuit 21, the steps can be made efficient. Other than these,advantages similar to that of the first embodiment can be achieved.

[0052] (Third Embodiment)

[0053] In the third embodiment shown in FIG. 5, a pad 12 is exposed tothe side of the surface of the sensor chip 10 at an end portion of theelectrode lead-out portion 3 d connected to the detecting portions 3 athrough 3 c of the sensor chip 10. An intermediary board 50 constitutingan intermediary member is arranged above the surface of the sensor chip10. FIG. 6 shows a perspective view of the intermediary board 50. Theintermediary board 50 is formed with an opening portion 51 having a sizesmaller than a planar shape of the substrate 1 of the sensor chip 10 andequal to or larger than an area corresponding to the detecting portions3 a through 3 c. The opening portion 51 is constituted such that a face51 a in side wall faces of the opening portion 51 disposed in a flowdirection of the fluid and deepened toward the center of the openingportion 51.

[0054] By constituting the opening portion 51 in such a shape, the fluidis made to flow smoothly above the detecting portions 3 a through 3 c.The intermediary board 50 is arranged above the surface 1 a of thesubstrate 1 such that the heater 3 a, the temperature measuring body 3 band the fluid thermometer 3 c constituting the detecting portion areexposed from the opening portion 51 of the intermediary member 50.

[0055] An intermediary member conductor portion 52 is formed at the rearface 50 b which is opposed to the surface 1 a of the substrate 1 of thesensor chip 10. The control circuit 21 is formed at the rear face 50 bof the intermediary board 50, and the intermediary member conductorportion 52 and the control circuit 21 are electrically connected. Thepad 12 of the substrate 1 and the intermediary member conductor portion52 are electrically connected by a bump 53 or the like.

[0056] According to this embodiment, since the intermediary board 50 isused, connecting portions of the detecting portions 3 a through 3 c andoutside of the sensor chip 10 (control circuit 21 or the like) and thecontrol circuit 21 can be prevented from being exposed to the fluidflowing above the detecting portions 3 a through 3 c. Therefore, theplanar size of the sensor chip 10 can be reduced. The intermediary board50 is not as high as a partition wall, and therefore the intermediaryboard 50 does not affect significant influence on the flow of the fluid.

[0057] (Fourth Embodiment)

[0058] According to this fourth embodiment, as shown in FIG. 7, thecontrol circuit 21 is formed on the side of the rear face 20 b of thecircuit board 20 similar to the second embodiment. The intermediaryboard 50 is used similar to the third embodiment.

[0059] The intermediary board 50 is connected to the side of the surfaceof the sensor chip 10. The side of the rear face of the sensor chip 10is fixed to the side of the surface 10 a of the circuit board 20 via anadhesive member 54. The circuit board 20 and the base board 30 are fixedto offset. The base conductor portion 22 on the side of the rear face 20b of the circuit board 20 is exposed.

[0060] The intermediary conductor portion 52 of the intermediary board50 and the base conductor portion 22 of the circuit board 20 areelectrically connected by using a bonding wire 55. As a result, theintermediary member conductor portion 52 and the control circuit 21 areelectrically connected via the bonding wire 55. The detecting portions 3a through 3 c and the control circuit 21 are electrically connected. Thebonding can be carried out, for example, after stacking and fixing thesensor chip 10 and the circuit board 20.

[0061] (Fifth Embodiment)

[0062] In the fifth embodiment shown in FIG. 8, the detecting portions 3a through 3 c and the control circuit 21 are connected by using abonding wire without using the intermediary board.

[0063] As shown in FIG. 8, the sensor chip 10, the circuit board 20 andthe baseboard 30 are layered to offset respectively. At the rear face 1b of the substrate 1, a wiring 14 electrically connected to thesubstrate conductor portion 11 is exposed, and the exposed wiring 14 iselectrically connected to the base conductor portion 22 of the circuitboard 20 by a bonding wire 15.

[0064] (Sixth Embodiment)

[0065] In the first embodiment, particularly in the fabricating methodshown in FIGS. 3A through 3E, a semiconductor board of a silicon boardor the like is used as the substrate 1. In such a case, when theconductor 9 is formed directly on the inner wall face of the throughhole 8 in forming the substrate conductor portion 11, the conductor 9and the substrate 1 are electrically and thermally connected. It istherefore likely that leakage of current is caused from the conductor 9to the substrate 1, and a temperature distribution becomesinappropriate. This sixth embodiment shown in FIGS. 9A to 9D and FIGS.10A and 10C reduces this likelihood.

[0066] First, as shown in FIG. 9A, the substrate 1 comprising asemiconductor board is prepared, and the thin film layers 2, 3 and 4 areformed above the surface 1 a of the substrate 1. Specifically, afterforming the lower film 2 on the surface 1 a of the substrate 1comprising a silicon board or the like, the conductor film 3 comprisingPt, Ti, Ti—Ni, Ti—W, Cr or the like is formed. The heater 3 a, thetemperature measuring body 3 b, the fluid thermometer 3 c and theelectrode lead-out portion 3 d are formed by patterning the conductorfilm 3. Thereafter, the upper film 4 is formed above the conductor film3.

[0067] Next, the through hole 8 is formed to reach the conductor film 3in the thin film layers 2 through 4, that is, the electrode lead-outportion 3 d by penetrating the substrate 1 from a portion on the side ofthe rear face 1 b of the substrate 1 which is not formed with hollowcavity portion 6.

[0068] Specifically, the insulating film 5 comprising a silicon nitridefilm or the like is formed to open only at a portion which is to beformed with the through hole 8 on the side of the rear face 1 b of thesubstrate 1. As shown in FIG. 9A, the through hole 8 is formed bycarrying out etching operation by using an alkaline solution of TMAH(tetramethylammonium halide), KOH or the like until the conductor film 3in the thin film layers 2 through 4 is exposed with the insulating film5 as a mask.

[0069] Next, as shown in FIGS. 9B, 9C and 9D, an insulating film 60 forthrough hole is formed at an edge portion of an opening of the throughhole 8 on the side of the rear face 1 b of the substrate 1 and an innerwall face of the through hole 8.

[0070] Specifically, as shown in FIG. 9B, by etching by hydrogenfluoride, the insulating film 5 and the lower film 2 exposed from thethrough hole 8 to the side of the rear face 1 b of the substrate 1 areremoved. Then, as shown in FIG. 9C, the insulating film 60 for throughhole is formed over a total of the rear face 1 b of the substrate 1including the inner wall face of the through hole 8 by a sputteringprocess or a CVD process. The insulating film 60 comprises a siliconoxide film, a silicon nitride film or the like.

[0071] As shown in FIG. 9D, by using a photolithography process, aresist 61 is formed by patterning on the surface of the insulating film60 for through hole and an unnecessary portion of the insulating film 60for through hole is etched and removed with the resist 61 as a mask.Thereby, the insulating film 60 for through hole is formed at the edgeportion of the opening of the through hole 8 on the side of the rearface 1 b of the substrate 1 and the inner wall face of the through hole8.

[0072] Next, as shown in FIG. 10A, the hollow cavity portion 6 is formedby carrying out etching operation while leaving the thin film layers 2through 4 from the side of the rear face 1 b of the substrate 1, and thethin film portion 7 is formed on the hollow cavity portion 6.

[0073] Specifically, after removing the resist 61, the hollow cavityportion 6 is formed by carrying out anisotropic etching by using analkaline solution of TMAH or KOH with the insulating film 60 for throughhole comprising a silicon oxide film or a silicon nitride film as amask.

[0074] Next, as shown in FIGS. 10B and 10C, the base conductor portion11 is formed on the side of the rear face 1 b of the substrate 1 byforming a conductor 42 constituting a conductor film for through hole atthe surface of the insulating film 60 for through hole to be broughtinto contact with the conductor film 3 of the thin film layers 2 through4 via the through hole 8 from the side of the rear face 1 b of thesubstrate 1. Hereinafter, the conductor 42 is referred to as theconductor film 42.

[0075] Specifically, as shown in FIG. 10B, the conductor film 42 forthrough hole comprising a conductor film of Au, Ti or the like is formedby using a sputtering process, a CVD process, a vapor deposition processor the like from the side of the rear face 1 b of the substrate 1.Successively, as shown in FIG. 10C, the conductor film 42 for throughhole is patterned by etching, a lift off process or the like using aphotolithography process. By the patterning, the conductor film 42 forthrough hole is brought into contact with the conductor film 3 (3 d) viathe through hole 8 and is formed on the surface of the insulating film60 for through hole.

[0076] In this way, the conductor film 42 for through hole disposed atthe edge portion of the opening of the through hole 8 on the side of therear face 1 b of the substrate 1 is formed as the substrate conductorportion 11. The substrate conductor portion 11 is electrically connectedto the electrode lead-out portion 3 d via the conductor 9 at inside ofthe through hole 8. As a result, the substrate conductor portion 11 iselectrically connected to the detecting portions 3 a through 3 c.

[0077] Thereafter, also in the sixth embodiment, similar to the firstembodiment shown in FIG. 3E, the substrate conductor portion 11 and thebase conductor portion 22 are electrically connected via the bump 23.Thereafter, the base board 30 is prepared, and the side of the rear face20 b of the circuit board 20 is fixed to the base board 30 by theadhesive member 31.

[0078] According to the sixth embodiment, the insulating film 60 forthrough hole is interposed between the substrate 1 and the conductor 9and the substrate conductor portion 11, that is, between the substrate 1and the conductor film 42 for through hole. Accordingly, electrical andthermal insulation between the substrate 1 and the conductor film 42 forthrough hole can be maintained. Therefore, it is less likely thatleakage of current is caused from the conductor film 42 for through holeto the substrate 1 or the temperature distribution becomesinappropriate.

[0079] (Seventh Embodiment)

[0080] In the seventh embodiment shown in FIG. 11, the both boards 10and 20 are arranged in parallel substantially on the same plane.

[0081] The fluid flow sensor chip 10 shown in FIG. 11 is the same as thefluid flow sensor chip 10 shown in FIG. 1. The thin film layerscomprising the conductor film and the insulating film are formed on thesurface 1 a of the substrate 1, and the detecting portion for detectinga flow rate of fluid flowing above the surface 1 a of the substrate 1 isformed. Further, the thin film portion 7 comprising the thin film layersis formed above the hollow cavity portion 6 formed from the side of therear face 1 b of the substrate 1 while leaving the thin film layers andthe substrate conductor portion 11 electrically connected to thedetecting portion is formed on the rear face 1 b of the substrate 1.

[0082] In FIG. 11, the thin film layers and the conductor film and theinsulating films constituting the thin film layers and the detectingportion are not illustrated. However, even in this embodiment, thesensor chip 10 has the thin film layers 2 through 4, the conductor film3, the insulating films 2 and 4 constituting the thin film layers 2through 4 as well as the detecting portions 3 a through 3 c and theelectrode lead-out portion 3 d, which are shown in FIG. 1.

[0083] The circuit board 20 constituting the base is formed with thecontrol circuit 21 for controlling the detecting portion at the surface20 a similar to, for example, the circuit board 20 shown in FIG. 1.

[0084] The fluid flow sensor chip 10 and the circuit board 20 aremounted above one face of the base board 30. The base board 30 comprisesceramic or the like and one face thereof is formed with a base boardconductor portion 32 comprising a conductive material of Au, Cu or thelike.

[0085] The fluid flow sensor chip 10 is fixed on the one face of thebase board 30 at the rear face 1 b on the side of the substrate 1opposed to the surface 1 a. Specifically, the substrate conductorportion 11 formed on the rear face 1 b of the substrate 1 in the fluidflow sensor chip 10 and the base board conductor portion 32 aremechanically and electrically connected via the bump 23 comprising Au orthe like.

[0086] Meanwhile, the circuit board 20 is fixed onto the one face of thebase board 30 on the side of the rear face 20 b by adhesive or the like.The control circuit 21 disposed on the surface 20 a of the circuit board20 and the base board conductor portion 32 are electrically connectedvia a bonding wire 16 of Au, Al or the like formed by wire bonding.

[0087] A partition wall 110 is provided for partitioning flow of fluidbetween the fluid flow sensor chip 10 and the circuit board 20 on theone face of the base board 30 in order to prevent the control circuit 21from being exposed to the fluid. The partition wall 110 is fixed ontothe one face of the base board 30 by adhesive or the like.

[0088] The base board conductor portion 32 is formed on the one face ofthe base 30 from the side of the fluid flow sensor chip 10 to the sideof the circuit board 20 by passing the lower side of the partition wall110. Thereby, on the one face of the base board 30, the substrateconductor portion 11 and the control circuit 21 are electricallyconnected via the base board conductor portion 32 and the bonding wire16.

[0089] According to the fluid flow sensor shown in FIG. 11, the fluidflows above the surface 1 a of the substrate 1 along a directionorthogonal to the paper face in FIG. 11. The circuit board 20partitioned by the partition wall 110 is not exposed to the flow of thefluid.

[0090] According to this seventh embodiment, the substrate conductorportion 11 is formed on the rear face 1 b other than the surface 1 a ofthe substrate 1. Therefore, the connecting portion of the controlcircuit 21 and the detecting portions 3 a through 3 c can be preventedfrom being exposed to the fluid flowing above the detecting portions 3 athrough 3 c disposed at the surface 1 a of the substrate 1.

[0091] By providing the partition wall 110 between the fluid flow sensorchip 10 and the circuit board 20, the control circuit 21 in the circuitboard 20 is not exposed to the flow of the fluid. The partition wall 110is not provided on the surface of the substrate of the fluid flow sensorchip 10.

[0092] That is, the fluid flow sensor chip 10 is electrically connectedto the control circuit 21 via the substrate conductor portion 11 of therear face 1 b of the substrate 1. Therefore, the detecting portion isnot provided at one side of the partition wall. A portion for carryingout transmission and reception of electric signals between outside andthe detecting portion is not provided on other side thereof with thepartition wall provided at the surface of the board as a boundary.Therefore, it is not necessary to enlarge the planar size of thesubstrate 1.

[0093] In this way, according to the seventh embodiment, the partitionwall 110 need not be provided at the surface 1 a of the substrate 1constituting the fluid flow sensor chip 10.

[0094] Next, FIG. 12 shows a modification of the seventh embodiment,particularly a modification of electric connection between the controlcircuit 21 and the base board conductor portion 32 in the circuit board20.

[0095] In the example shown in FIG. 12, the control circuit 21 is formedon the surface 20 a of the circuit board 20, and the circuit board 20 isfixed onto one face of the base board 30 at the rear face 20 b on theside opposed to the surface 20 a. The control circuit 21 and the baseboard conductor portion 32 are electrically connected via the throughhole 24 provided to penetrate from the surface 20 a of the circuit board20 to the rear face 20 b.

[0096] A construction similar to the through hole 24 of the circuitboard 20 shown in FIG. 4 can be adopted for the through hole 24 of thecircuit board 20. By providing the conductor at inside of the throughhole 24, conduction between the surface 20 a and the rear face 20 b ofthe circuit board 20 can be achieved. The conductor at inside of thethrough hole 24 of the circuit board 20 and the base board conductorportion 32 can be connected by the bump 33.

[0097] (Eighth Embodiment)

[0098] In the eighth embodiment shown in FIG. 13, the sensor chip 10 andboard 20 are provided in parallel in a manner similar to the seventhembodiment. Further, similar to the first embodiment shown in FIG. 1,the fluid flow sensor chip 10 shown in FIG. 13 is formed with the thinfilm layers 2 through 4 comprising the conductor film 3 and theinsulating films 2 and on the surface 1 a of the substrate 1. The chip10 is formed with the detecting portions 3 a through 3 c for detecting aflow rate of fluid flowing above the surface 1 a of the substrate 1 bythe conductive film 3 and formed with the thin film portion 7 comprisingthe thin film layers 2 through 4 above the hollow cavity portion 6formed from the side of the rear face 1 b of the substrate 1 whileleaving the thin film layers 2 through 4.

[0099] Here, the sensor chip 10 of FIG. 13 is formed with a substrateconductor portion 11 a electrically connected to the detecting portions3 a through 3 c. The substrate conductor portion 11 a formed there canbe constituted, for example, by a conductor film of Au, Al or the likeformed on the surface of the electrode lead-out portion 3 d in FIG. 2.The conductor film can be connected to the electrode lead-out portion 3d by forming a contact hole at the upper film 4 of the thin film layers2 through 4.

[0100] Meanwhile, the circuit board 20 shown in FIG. 13 is formed withthe control circuit 21 and a base conductor portion 22 a conducted tothe control circuit 21. The base board 30 shown in FIG. 13 is not formedwith the base board conductor portion at a face thereof mounted with thefluid flow sensor chip 10 and the circuit board 20.

[0101] The fluid flow sensor chip 10 is fixedly attached onto the oneface of the base board 30 at the rear face 1 b of the substrate 1 viathe adhesive member 31, and the circuit board 20 is fixedly connectedonto the one face of the base board 30 at the rear face 20 b via theadhesive member 31.

[0102] As shown in FIG. 13, there is bridged a connecting member 120 forelectrically connecting the substrate conductor portion 11 a and thecontrol circuit 21. The connecting member 120 comprises a silicon boardor the like, the planar size thereof being smaller than that of thesubstrate 1 and the thickness thereof being equivalent or smaller thanthe thickness of the substrate 1. The rear face of the connecting member120 is formed with a connecting member conductor portion 121 comprisinga conductive material of Au, Ni or the like.

[0103] As shown in FIG. 13, the substrate conductor portion 11 a iscovered with the connecting member 120. Further, the base conductorportion constituting an electric connecting portion between the controlcircuit 21 and the connecting member 120 is covered. The connectingconductor portion 120 and the substrate conductor portion 11 a as wellas the connecting conductor portion 120 and the base conductor portion22 a are electrically and mechanically connected by bumps 122 comprisingAu or the like.

[0104] According to the fluid flow sensor shown in FIG. 13, fluid flowsabove the surface 1 a of the substrate 1 along a direction orthogonal tothe paper face in FIG. 13. The electric connecting portions such as thesubstrate conductor portion 11 a and the base conductor portion 22 acovered with the connecting member 120 are prevented from being exposedto the flow of the fluid.

[0105] According to the connecting member 120, the planar size issmaller than that of the substrate 1 and the thickness is equivalent toor smaller than the thickness of the substrate 1. Therefore, the flow ofthe fluid is hardly disturbed. Therefore, it is not necessary to enlargea distance between the detecting portions 3 a through 3 c and theconnecting member 120 in the fluid flow sensor chip 10.

[0106] (Ninth Embodiment)

[0107] The ninth embodiment is directed to protect the substrate frombeing damaged or broken due to a thin layered film structure layeredwith the insulating films and the conductor film. The manufacturingmethod of the ninth embodiment is shown in FIGS. 14A to 14C.

[0108] First, the substrate 1 is prepared, and a trench 70 having apredetermined depth is formed at a portion of the substrate 1 which isnot formed with the hollow cavity portion 6 from the side of the surface1 a of the substrate 1.

[0109] Specifically, the lower film 2 for constituting the thin filmlayers 2 through 4 at the surface 1 a of the substrate 1 and the lowerfilm 2 disposed at a portion which is to be formed with the trench 70 isremoved by etching or the like. Successively, the trench 70 is formed bycarrying out trench etching of RIE (reactive ion etching) or the likefrom the surface 1 a of the substrate 1 with the lower film 2 as a mask.

[0110] Next, an insulating film 62 is formed on an inner wall face ofthe trench 70. Specifically, the insulating film 62 can be formed bythermal oxidation or the like. Next, a conductor 63 for trench isembedded at inside of the trench 70 formed with the insulating film 62.Specifically, the conductor 63 can be embedded by a sputtering process,a CVD process, a vapor deposition process or the like by usingpolycrystal silicon, Au, Al or the like.

[0111] The thin film layers 2 through 4 are formed on the surface 1 a ofthe substrate 1 so that the detecting portions 3 a through 3 c and theconductor 63 are electrically connected. Specifically, the lower film 2is formed except that of the portion of the trench 70. Therefore, thedetecting portions 3 a through 3 c and the electrode lead-out portion 3d conducted thereto are formed by forming to pattern the conductor film3 thereon.

[0112] Here, the electrode lead-out portion 3 d is formed at the portionof the trench 70, the electrode lead-out portion 3 d and the conductor63 for trench are electrically connected. As a result, the detectingportions 3 a through 3 c and the conductor 63 for trench areelectrically connected. By forming the upper film 4, the thin filmlayers 2 through 4 are formed at the surface 1 a of the substrate 1.

[0113] Next, an opening portion 71 reaching a bottom portion of thetrench 70 is formed by carrying out etching from the side of the rearface 1 b of the substrate 1.

[0114] Specifically, the insulating film 5 is formed so that an area ofthe rear face 1 b of the substrate 1 corresponding to the trench 70 isopened. The insulating film 5 can be formed to pattern by forming asilicon nitride film or the like and carrying out etching using thephotolithography technology.

[0115] Next, the opening portion 71 is formed by carrying outanisotropic etching by using an alkaline solution of TMAH, KOH or thelike until the insulating film 62 and the conductor 63 for trench atinside of the trench 70 are exposed with the insulating film 5 as amask.

[0116] Successively, an insulating film 64 for opening portion is formedat an edge portion of the opening of the opening portion 71 on the sideof the rear face 1 b of the substrate 1 and the inner wall face of theopening portion 71. Specifically, the insulating film 64 for openingportion is formed by forming a silicon oxide film or the like by asputtering process, a CVD process or the like.

[0117] Similar to FIG. 9D, an unnecessary portion of the insulating film64 for opening portion is etched to remove along with the insulatingfilm 5 by etching by hydrogen fluoride or the like using thephotolithography process.

[0118] In this occasion, the insulating film 64 for opening portiondisposed at the bottom portion of the opening portion 71 opened to theside of the rear face 1 b of the substrate 1 is selectively removed, andthe conductor 63 for trench is exposed to the side of the rear face 1 bof the substrate 1. The insulating film 5 and the insulating film 64 foropening portion are patterned to open a portion to be formed with thehollow cavity portion 6.

[0119] Next, the hollow cavity portion 6 is formed by carrying outetching from the side of the rear face 1 b of the substrate 1 whileleaving the thin film layers 2 through 4, and the thin film portion 7 isformed above the hollow cavity portion 6.

[0120] Specifically, the hollow cavity portion 6 is formed by carryingout anisotropic etching using an alkaline solution of TMAH or KOH or thelike by constituting a mask by the insulating film 5 and the insulatingfilm 64 for opening portion which have been patterned to open theportion to be formed with the hollow cavity portion 6.

[0121] Next, the substrate conductor portion 11 is formed from the sideof the rear face 1 b of the substrate 1 by forming a conductor 65 foropening portion at a surface of the insulating film 64 to be broughtinto contact with the conductor 63 for trench via the opening portion 71from the side of the rear face 1 b of the substrate 1.

[0122] Specifically, the conductor film 65 comprising a conductor filmof Au, Ti or the like is formed from the side of the rear face 1 b ofthe substrate 1 by using a sputtering process, a CVD process, a vapordeposition process or the like. The conductor film 65 is patterned byetching using a photolithography process or a lift off process or thelike. Thereby, the conductor film 65 for opening portion is formed in ashape brought into contact with the conductor film 63 for trench via theopening portion 71 and formed on the surface of the insulating film 64.

[0123] In this way, the conductor film 65 disposed at the edge portionof the opening of the opening portion 71 on the side of the rear face 1b of the substrate 1 as the substrate conductor portion 11. Thesubstrate conductor portion 11 is electrically connected to theelectrode lead-out portion 3 d via the conductor film 65 at inside ofthe opening portion 71 and the conductor 63 for trench at inside of thetrench 70. As a result, it is electrically connected to the detectingportions 3 a through 3 c.

[0124] Thereafter, also in the ninth embodiment, by connecting the fluidflow sensor chip 10 to the circuit board 20 via the substrate conductorportion 11 and mounting the circuit board 20 to the base board 30, thefluid flow sensor 100 can be completed.

[0125] According to the fabricating method, by previously forming thetrench of a certain degree of depth from the surface 1 a of thesubstrate 1 and embedding the trench 70 by the conductor 63 for trench,a sufficient thickness is ensured and mechanical strength is alsoensured. Therefore, destruction of the substrate 1 can be restrained infabricating or using the substrate 1.

[0126] In the fabricating method of the ninth embodiment, etching forforming the opening portion 71 from the side of the rear face 1 b of thesubstrate 1 and etching for forming the hollow cavity portion 6 maysimultaneously be carried out. Thereby, simplification of steps can beachieved.

[0127] Specifically, in forming the insulating film 5 constituting themask for forming the opening portion 71 at the rear face 1 b of thesubstrate 1, at the insulating film 5, the insulating film 5 is formedto pattern to open the area corresponding to the trench 70 and theportion to be formed with the hollow cavity portion 6.

[0128] The opening portion 71 and the hollow cavity portion 6 cansimultaneously be formed by carrying out anisotropic etching using analkaline solution of TMAH, KOH or the like with the insulating film 5 asthe mask.

[0129] With regard to forming the insulating film 64 and the conductorfilm 65, which is carried out at a later step, the films can selectivelybe formed by using normal photolithography process, etching technology,lift off process or the like, and the structure shown in FIG. 14C cansimilarly be formed.

[0130] (Tenth Embodiment)

[0131] According to the method of forming the through hole 8 as shown inFIGS. 3A through 3E, FIGS. 9A through 9D and FIGS. 10A through 10C, thesemiconductor board is used as the substrate 1. The substrate 1 ispenetrated from the side of the rear face 1 b of the substrate 1 bysingle operation of anisotropic etching. In this case, the inner wallface of the through hole 8 formed by the anisotropic etching is formedin a tapered shape widening toward the side of the rear face 1 b of thesubstrate 1 as shown in FIGS. 9A through 9D.

[0132] Therefore, the opening area of the through hole 8 is enlarged. Asa result, a space occupied at the substrate 1 by the substrate conductorportion 11 is also enlarged. Therefore, the large space is notpreferable for further promoting small-sized formation of the substrate1 and accordingly of the fluid flow sensor chip 10. The tenth embodimentprovides a fabrication method as a measure for resolving such a problem.

[0133] First, as shown in FIG. 15A, the substrate 1 is prepared, and afirst opening portion 81 of a predetermined depth is formed at a portionof the substrate 1 which is not formed with the hollow cavity portion 6by carrying out anisotropic etching from the side of the surface 1 a ofthe substrate 1.

[0134] Specifically, the first opening portion 81 is formed by carryingout anisotropic etching using an alkaline solution of TMAH, KOH or thelike by masking a portion other than a portion to be etched.

[0135] Next, the thin film layers 2 through 4 are formed at the surface1 a of the substrate 1 including the inner wall face of the firstopening portion 81. In this occasion, according to the example shown inFIG. 15A, the electrode lead-out portion 3 d in the conductor film 3constituting the thin film layers is formed on the inner wall face ofthe first opening portion 81.

[0136] Next, the insulating film 5 is formed as a mask for forming asecond opening portion 82. The insulating film 5 is provided with ashape in which an area of the rear face 1 b of the substrate 1corresponding to the first opening portion 81 is opened and can beformed to pattern by forming a silicon nitride film or the like andcarrying out etching using the photolithography technology.

[0137] Next, the second opening portion 82 is formed to penetrate to thefirst opening portion 81 by carrying out anisotropic etching from theside of the rear face 1 b of the substrate 1.

[0138] Specifically, the second opening portion 82 is formed by carryingout anisotropic etching using an alkaline solution of TMAH, KOH or thelike to expose the lower film 2 of the thin film layers 2 through 4 atinside of the first opening portion 81 by constituting a mask by theinsulating film 5.

[0139] Next, an insulating film 83 for second opening portion is formedat an edge portion of an opening of the second opening portion 82 on theside of the rear face 1 b of the substrate 1 and an inner wall face ofthe second opening portion 82. Specifically, the insulating film 83 forsecond opening is formed by forming a silicon oxide film or the like bya sputtering process, a CVD process or the like.

[0140] An unnecessary portion of the insulating film 83 is removed byetching along with the insulating film 5 by etching by hydrogen fluorideor the like using the photolithography process or the like.

[0141] At this occasion, the insulating film 83 disposed at the bottomportion of the second opening portion 82 opening to the side of the rearface 1 b of the substrate 1 and the lower film 2 of the thin film layers2 through 4 are selectively removed. The conductor film 3 of the thinfilm layer is exposed to the side of the rear face 1 b of the substrate1. The insulating film 5 and the insulating film 83 for second openingportion are patterned to open a portion to be formed with the hollowcavity portion 6.

[0142] Next, the hollow cavity portion 6 is formed by carrying outanisotropic etching from the side of the rear face 1 b of the substrate1 while leaving the thin film layers 2 through 4. The thin film portion7 is formed on the hollow cavity portion 6.

[0143] Specifically, the hollow cavity portion 6 is formed by carryingout anisotropic etching using an alkaline solution of TMAH, KOH or thelike by constituting a mask by the insulating film 5 and the insulatingfilm 83 for second opening portion which are patterned to open theportion to be formed with the hollow cavity portion 6.

[0144] Next, by forming a conductor 84 at a surface of the insulatingfilm 83 to be brought into contact with the conductor film 3 (electrodelead-out portion 3 d) of the thin film layers 2 through 4 from the sideof the rear face 1 b of the substrate 1 via the second opening portion82, the substrate conductor portion 11 is formed on the side of the rearface 1 b of the substrate 1.

[0145] Specifically, the conductor film 84 comprising a conductor filmof Au, Ti or the like is formed from the side of the rear face 1 b ofthe substrate 1 by using a sputtering process, a CVD process, a vapordeposition process or the like. The conductor film 84 is patterned byetching by using the photolithography process or a lift off process orthe like. Thereby, the conductor film 84 for second opening portion isformed in a shape brought into contact with the conductor film 3 (3 d)via the second opening portion 82 and formed at a surface of theinsulating film 83 for second opening portion.

[0146] In this way, the conductor film 84 disposed at an edge portion ofan opening of the second opening portion 82 is formed on the side of therear face 1 b of the substrate 1 as the substrate conductor portion 11.The substrate conductor portion 11 is electrically connected to theelectrode lead-out portion 3 d via the conductor film 84 at inside ofthe second opening portion 82 and as a result, electrically connected tothe detecting portions 3 a through 3 c.

[0147] Thereafter, also in the tenth embodiment, the fluid flow sensor100 can be completed by connecting the fluid flow sensor chip 10 to thecircuit board 20 via the substrate conductor portion 11 and mounting thecircuit board 20 to the base board 30.

[0148] According to this fabricating method, the first opening portion81 of a certain degree of depth is previously formed from the surface 1a of the substrate 1 by anisotropic etching. Successively, the secondopening portion 82 is formed from the rear face 1 b of the substrate 1by anisotropic etching, and the first and the second opening portions 81and 82 are communicated with each other.

[0149] Opening areas of the respective first and second opening portions81 and 82 can be made smaller than an opening area of a through holeformed by penetrating the substrate 1 from the side of the rear face 1 bof the substrate 1 by single operation of anisotropic etching. As aresult, the area necessary for the substrate conductor portion 11 isreduced.

[0150] According to the fabricating method of the tenth embodiment,anisotropic etching for forming the second opening portion 82 from theside of the rear face 1 b of the substrate 1 and the anisotropic etchingfor forming the hollow cavity portion 6 may simultaneously be carriedout. Thereby, simplification of steps can be achieved. Specifically, theanisotropic etching can be carried out in conformity with the method ofsimultaneously etching the opening portion and the hollow cavity portionaccording to the ninth embodiment.

[0151] (Eleventh Embodiment)

[0152] In the above embodiments, the substrate conductor portion 11 canbe formed from the side of the rear face 1 b of the substrate 1. Thatis, the respective through holes 8 can also be arranged in one row in adirection orthogonal to a direction of extending the lead portion.However, when the through holes 8 are formed by anisotropic etching, asdescribed at beginning of the tenth embodiment, the opening area islarge. Therefore, there is a limit in arranging a plurality of thethrough holes 8 in view of space thereof. In this case, when thethickness of the substrate 1 is thinned, the opening area of the throughhole 8 can also be reduced. However, the strength of the substrate 1 islowered.

[0153] The eleventh embodiment provides a fluid flow sensor, which isconstructed as shown in FIG. 16 to overcome the above problem. As shownin FIG. 16, the detecting portions 3 a through 3 c for detecting a flowrate of a fluid flowing above the surface 1 a of the substrate 1 isformed on the surface 1 a of the substrate 1. On the surface 1 a of thesubstrate 1, the electrode lead-out portions 3 d are formed as aplurality of pieces of lead portions electrically connected to thedetecting portions 3 a through 3 c to extend from the detecting portions3 a through 3 c toward a peripheral portion at an end side of thesubstrate 1.

[0154] A plurality of pieces of the substrate conductor portions 11corresponding to the plurality of pieces of electrode lead-out portions3 d is formed on the rear face 1 b of the substrate 1. Here, the throughholes 8 are formed to penetrate from the side of the rear face 1 b ofthe substrate 1 to the side of the surface 1 a of the substrate 1 byanisotropic etching at portions connecting the respective electrodelead-out portions 3 d and the substrate conductor portions 11.

[0155] In this embodiment, in a manner similar to that shown in FIGS. 3Athrough 3E and FIGS. 10A through 10C, the through hole 8 is providedwith the conductor at inside of the through hole 8. Thereby, therespective electrode lead-out portion 3 d and the substrate conductorportion 11 are electrically connected via the through hole 8.

[0156] In this case, as shown in FIG. 16, the respective through holes 8are arranged alternately in the direction of extending the electrodelead-out portions 3 d. That is, the respective through holes 8 arearranged not in one row in the direction orthogonal to the direction ofextending the electrode lead-out portion 3 d but with steppeddifferences thereamong.

[0157] By arranging the respective through holes 8 alternately in thedirection of extending the electrode lead-out portion 3 d, in comparisonwith the case of arranging the respective holes 8 in one row in thedirection orthogonal to the direction of extending the electrodelead-out portion 3 d, the respective through holes 8 can efficiently bearranged in view of space.

[0158] Therefore, according to the eleventh embodiment, it is possibleto realize the constitution of the fluid flow sensor chip preferable forarranging the through holes 8, and accordingly the substrate conductorportions 11 in a limited narrow space with high density.

[0159] According to this embodiment, transmission and reception ofelectric signals between outside of the fluid flow sensor chip 10 andthe detecting portions 3 a through 3 c can be carried out via thesubstrate conductor portions 11 on the side of the rear face 1 b of thesubstrate 1. Therefore, the planar size of the fluid flow sensor chip 10can be reduced similar to the first embodiment and the like.

[0160] (Other Embodiment)

[0161] In the first embodiment, a spacing between the sensor chip 10 andthe circuit board 20 may be molded by an adhesive member of epoxyspecies or the like. Thereby, the control circuit 21 can be preventedfrom malfunctioning by small deposit dust in the vicinity of the controlcircuit 21 or by undergoing influence of the humidity.

[0162] An adhesive member of epoxy resin or the like may be filled in agap produced between the sensor chip 10 and the portion layered with theintermediary board 50. Thereby, connection between the sensor chip 10and the intermediary board 50 is reinforced. The control circuit 21 neednot be arranged on the rear face in the vicinity of the sensor chip 10in the intermediary board 50 but may electrically be connected to thecontrol circuit 21 at a remote position by a bonding wire.

[0163] The substrate conductor portion 11 at the rear face 1 b of thesubstrate 11 may electrically be connected to the control circuit 21 orother circuit by carrying out direct bonding.

[0164] The substrate conductor portion 11 and the control circuit 21 mayelectrically be connected via a bonding wire 29 by connecting thesubstrate conductor portion 11 of the sensor chip 10 to an end portionof a wiring 28 above the circuit board 20 and electrically connectingthe wiring 28 and the control circuit 21 by the bonding wire 29 or thelike as shown in FIG. 17 without arranging the sensor chip 10 above aportion of the circuit board 20 formed with the control circuit 21.

[0165] The detecting portion 3 a through 3 c at the surface 1 a of thesubstrate 1 and the substrate conductor portion 11 may electrically beconnected by forming a wiring on an outer surface of the substrate 1from the surface 1 a of the substrate 1 of the sensor chip 10 to a sideface thereof, further to the rear face 1 b without providing the throughhole 8. The substrate conductor portion 11 may be formed not on the rearface 1 b of the substrate 1 but, for example, on the side face of thesubstrate 1, and a wiring may be formed on the outer surface of thesubstrate 1 from the detecting portions 3 a through 3 c to the substrateconductor portion 11.

[0166] A casing containing the fluid flow sensor may be utilized as theintermediary board 50 the third embodiment. That is, the control circuit21 may be formed at an inner surface of the casing or by forming awiring at the inner surface of the casing, the wiring may electricallybe connected to the control circuit 21 arranged at a portion other thanthe inner surface of the casing. Thereby, a number of necessary parts ofthe fluid flow sensor 100 can be reduced.

[0167] Although the conductors 9 and 25 are provided at the inner wallfaces of the through holes 8 and 24 in the above embodiments, thethrough holes 8 and 24 may be embedded with conductors. When possible,the control circuit 21 may directly be provided on the rear face 1 b ofthe substrate 1 and may electrically be connected to the substrateconductor portion 11.

What is claimed is:
 1. A fluid flow sensor comprising: a fluid flowsensor chip including a board and detecting portions formed on a firstsurface of the board for detecting a flow rate of a fluid flowing abovethe first surface of the board, wherein the fluid flow sensor chipfurther includes a substrate conductor portion electrically connected tothe detecting portions and formed on a face of a second surface of theboard other than the first surface.
 2. The fluid flow sensor as in claim1, further comprising: a control circuit electrically connected to thesubstrate conductor portion for controlling the detecting portions.
 3. Afluid flow sensor comprising: a fluid flow sensor chip including a boardhaving a first surface and formed with detecting portions for detectinga flow rate of a fluid flowing above the first surface of the board; anda base formed with a control circuit for controlling the detectingportions, wherein the fluid flow sensor chip is formed with a substrateconductor portion electrically connected to the detecting portions on aface of a second surface of the board other than the first surface, andwherein the substrate conductor portion and the control circuit areelectrically connected such that the control circuit is arranged on aplane different from the surface of the board.
 4. The fluid flow sensoras in claim 3, wherein: the control circuit is formed on a side of afirst surface of the base; and the side of the first surface of theboard is arranged in opposition to the second surface of the board tothereby layer the board and the base.
 5. The fluid flow sensor as inclaim 3, further comprising: a base board fixed to the board and thebase; and an adhesive member for attaching the base and the base board,wherein the control circuit is formed on a side of a second surface ofthe base, wherein the second surface of the base is arranged inopposition to the board to thereby layer the board and the base, andwherein the side of the second surface of the base is fixed to the baseboard.
 6. The fluid flow sensor as in claim 3, wherein the substrateconductor portion and the control circuit are electrically connected viaa bonding wire.
 7. The fluid flow sensor as in claim 3, wherein: athrough hole is formed in the board; the substrate conductor portion isformed on the side of the second surface of the board; and the detectingportions and the substrate conductor portion are electrically connectedvia a conductor formed on an inner wall face of the through hole.
 8. Afluid flow sensor comprising: a fluid flow sensor chip including a boardhaving a first surface, and formed with detecting portions for detectinga flow rate of a fluid flowing above the first surface of the board; anintermediary member smaller than a planar shape of the board andprovided with an opening portion having a size larger than an areacorresponding to the detecting portions, wherein the intermediary memberis arranged above the first surface of the board such that the detectingportions are exposed from the opening portion, and wherein a padelectrically connected to the detecting portions on the first surface ofthe board and an intermediary member conductor portion of theintermediary member formed on a face of the intermediary member inopposition to the first surface of the board are electrically connected.9. The fluid flow sensor as in claim 8, further comprising: a controlcircuit formed on the face of the intermediary member for controllingthe detecting portions and electrically connected to the intermediarymember conductor portion.
 10. The fluid flow sensor as in claim 9,wherein the intermediary conductor portion and the control circuit areelectrically connected via a bonding wire.
 11. The fluid flow sensor asin claim 8, further comprising: thin film layers formed on the firstsurface of the board and above a hollow cavity portion formed from thesecond surface of the board while leaving the thin film layers and thedetecting portions.
 12. The fluid flow sensor as in claim 4, furthercomprising: thin film layers formed on the first surface of the boardand above a hollow cavity portion formed from the second surface of theboard while leaving the thin film layers, wherein the fluid flow sensorchip and the base are layered with a gap therebetween.
 13. A fluid flowsensor comprising: a fluid flow sensor chip including a board anddetecting portions formed on a first surface of the board for detectinga flow rate of a fluid; a base formed with a control circuit forcontrolling the detecting portions; and a base board for mounting thefluid flow sensor chip and the base, wherein the fluid flow sensor chipis fixed onto one face of the base board at a second surface of theboard on a side opposed to the second surface, wherein a partition wallis provided for partitioning a flow of the fluid between the fluid flowsensor chip and the base above the one face of the base board such thatthe control circuit is not exposed to the fluid, wherein a base boardconductor portion formed from a side of the fluid flow sensor chip to aside of the base by passing a lower side of the partition wall is formedabove the one face of the base board, wherein a substrate conductorportion electrically connected to the detecting portions is formed onthe second face of the board, and wherein the substrate conductorportion and the control circuit are electrically connected via the baseboard conductor portion above the one face of the base board.
 14. Thefluid flow sensor as in claim 13, wherein: the control circuit is formedon a first surface of the base; the base is fixed onto the one face ofthe base board at a second face thereof on a side opposed to the oneface; and the control circuit and the base board conductor portion areelectrically connected via a bonding wire.
 15. The fluid flow sensor asin claim 13, wherein: the control circuit is formed on a first surfaceof the base; the base is fixed onto the one face of the base board at asecond surface thereof on a side opposed to the one face; and thecontrol circuit and the base conductor portion are electricallyconnected via a through hole provided to penetrate the base.
 16. A fluidflow sensor comprising: a fluid flow sensor chip including a board anddetecting portions formed on a first surface of the board for detectinga flow rate of a fluid flowing above the first surface of the board; abase formed with a control circuit for controlling the detectingportions; and a base board mounting the fluid flow sensor chip and thebase, wherein the fluid flow sensor chip is formed with a substrateconductor portion electrically connected to the detecting portions atthe first surface of the board and fixed to a one face of the base boardat a second surface of the board; wherein a connecting member forelectrically connecting the base conductor portion and the controlcircuit is bridged between the board and the base; wherein a portionelectrically connecting the substrate conductor portion and the controlcircuit and the connecting member is covered by the connecting member;wherein a planar size of the connecting member is smaller than a planarsize of the board and a thickness thereof is equivalent to or smallerthan a thickness of the board.
 17. A fluid flow sensor comprising: afluid flow sensor chip including a board and detecting portions formedon a first surface of the board for detecting a flow rate of a fluidflowing above the first surface of the board, wherein the first surfaceof the board is formed with a plurality of pieces of lead portionselectrically connected to the detecting portions to extend from thedetecting portions to a peripheral portion on a side of one end of theboard, wherein a second surface of the board opposite the first surfaceis formed with a plurality of pieces of substrate conductor portionscorresponding to the plurality of pieces of lead portions, whereinrespectives of the lead portions and the substrate conductor portionsare electrically connected via through holes formed from a side of thesecond surface of the board to the second surface of the board byanisotropic etching, and wherein respectives of the through holes arearranged alternately in a direction of extending the lead portion.
 18. Amethod of fabricating a fluid flow sensor which is formed with thin filmlayers comprising a conductor film and an insulating film on a firstsurface of a board, formed with detecting portions for detecting a flowrate of a fluid by the conductor film, formed with a thin film portioncomprising the thin film layers above a hollow cavity portion formedfrom a side of a second surface in the board while leaving the thin filmlayers, and formed with a substrate conductor portion electricallyconnected to the detecting portions at the second surface of the board,the method comprising steps of: preparing the board and forming the thinfilm layers above the first surface of the board; forming the thin filmportions above the hollow cavity portion by forming the hollow cavityportion by etching the board from the side of the second surface of theboard while leaving the thin film layers; forming a through holereaching the conductor film by penetrating the board from a portion ofthe second surface of the board where the hollow cavity portion is notformed; and forming a conductor on an inner wall face of the throughhole and forming the substrate conductor portion on the side of thesecond surface of the board.
 19. A method of fabricating a fluid flowsensor which is formed with thin film layers comprising a conductor filmand an insulating film on a first surface of a board, formed withdetecting portions for detecting a flow rate of a fluid by the conductorfilm, formed with a thin film portion comprising the thin film layersabove a hollow cavity portion formed from a side of a second surface inthe board while leaving the thin film layers, and formed with asubstrate conductor portion electrically connected to the detectingportions at the second surface of the board, the method comprising stepsof: preparing the board and forming the thin film layers on the firstsurface of the board; forming a through hole reaching the conductor filmof the thin film layers by penetrating the board from a portion on theside of the second surface of the board where the hollow cavity portionis not formed; forming an insulating film for the through hole at anedge portion of an opening of the through hole on the side of the secondsurface of the board and on an inner wall face of the through hole;forming the hollow cavity portion by etching the board from the side ofthe second surface of the board while leaving the thin film layers andforming the thin film portion above the hollow cavity portion; andforming the substrate conductor portion on the side of the secondsurface of the board by forming a conductor film for the through hole ata surface of the insulating film for the through hole from the side ofthe second surface of the board to be brought into contact with theconductor film of the thin film layers via the through hole.
 20. Amethod of fabricating a fluid flow sensor which is formed with thin filmlayers comprising a conductor film and an insulating film on a firstsurface of a board, formed with detecting portions for detecting a flowrate of a fluid by the conductor film, formed with a thin film portioncomprising the thin film layers above a hollow cavity portion formedfrom a side of a second surface in the board while leaving the thin filmlayers, and formed with a substrate conductor portion electricallyconnected to the detecting portions at the second surface of the board,the method comprising steps of: preparing the board and forming a trenchhaving a predetermined depth from a side of the first surface of theboard at a portion of the board where the hollow cavity portion is notformed; forming an insulating film for the trench at an inner wall faceof the trench; embedding a conductor for the trench to an inner portionof the trench formed with the insulating film from the side of the firstsurface of the board; forming the thin film layers to provide a state ofelectrical connection between the detecting portions and the conductor;forming an opening portion reaching a bottom portion of the trench byetching the board from a side of a second surface of the board; formingthe thin film portion above the hollow cavity portion by forming thehollow cavity portion by etching the board from the side of the secondsurface of the board while leaving the thin film layers; forming aninsulating film for the opening portion at an edge portion of an openingof the opening portion on the side of the second surface of the boardand an inner wall face of the opening portion; and forming the substrateconductor portion on the side of the second surface of the board byforming a conductor for the opening portion at a surface of theinsulating film for the opening portion to be brought into contact withthe conductor via the opening portion from the side of the secondsurface of the board.
 21. The method of fabricating a fluid flow sensoras in claim 20, wherein etching for forming the opening portion andetching for forming the hollow cavity portion are simultaneously carriedout.
 22. A method of fabricating a fluid flow sensor which is formedwith thin film layers comprising a conductor film and an insulating filmon a first surface of a board, formed with detecting portions fordetecting a flow rate of a fluid by the conductor film, formed with athin film portion comprising the thin film layers above a hollow cavityportion formed from a side of a second surface in the board whileleaving the thin film layers, and formed with a substrate conductorportion electrically connected to the detecting portions at the secondsurface of the board, the method comprising steps of: preparing theboard and forming a first opening portion having a predetermined depthby anisotropically etching the board from a side of the first surface ofthe board at a portion where the hollow cavity portion is not formed;forming the thin film layers on the first surface of the board includingan inner wall face of the opening portion; forming a second openingportion penetrated to the first opening portion by anisotropicallyetching the board from a side of a second surface of the board oppositethe first surface; forming the thin film portion above the hollow cavityportion by forming the hollow cavity portion by anisotropically etchingthe board while leaving the thin film layers from a side of the secondsurface of the board; forming an insulating film for the second openingportion at an edge portion of an opening of the second opening portionon the side of the second surface of the board and an inner wall face ofthe second opening portion; and forming the substrate conductor portionon the side of the second surface of the board by forming a conductorfor the second opening portion on a surface of the insulating film to bebrought into contact with the conductor film of the thin film layers viathe second opening portion from the side of the second surface of theboard.
 23. The method of fabricating a fluid flow sensor as in claim 22,wherein anisotropic etching for forming the second opening portion andanisotropic etching for forming the hollow cavity portion aresimultaneously carried out.